1. Field of the Invention
This invention pertains to the generation of maps to be displayed on a CRT by digital processing of digitally encoded geodetic and cultural data that defines the environment to be mapped.
2. Description of the Prior Art
A special problem exists in providing a night-flying aviator with information on the terrain over which he is flying. Scheduled flights to large airports may be adequately served by elaborate instrumentation and flight control instructions, although knowledge of the surrounding terrain is desirable. But low flying military aircraft, or those performing emergency services in sparsely settled areas, rely very much on visual contact; illumination sufficient for seeing conventional maps may impair dark adaption and many maps may be needed to cover the possible range of modern aircraft. A self-luminous display like the face of a cathode ray tube does not require illumination of the background, and may be biased down to the very lower limit of visibility so that it impairs dark adaptation negligibly. Television-type techniques can obviously be employed to present an image of a printed map; a flying-spot scanner has been employed to scan holograms in a similar application. Such a display is clearly limited by an available number of maps and has limited flexibility in the choice of data to be displayed. Generation of maps from stored digital environmental data is known in the art; simulation of radar presentations from similar data is also known and described as "radar mapping" (somewhat loosely since the radar presentation itself may well not be a true map). The applicant's U.S. Pat. Nos. 3,769,442 and 3,883,861 and 4,017,985, and 3,892,051 of Bunker (all assigned to the assignee of this application) variously describe the preparation of digital bases for terrain simulation and the generation of simulated images for pilot training. None of these inventions is subject to size, weight and power constraints of airborne equipment.
Another important constraint to be met is time. A general purpose digital computer can perform all the functions required to generate a map display but, because of the large amounts of data to be processed, it would take many minutes and in some cases over an hour, to generate a single display. This, in airborne applications, is unacceptable. Thus special, dedicated, processing loops to maximize data throughput are required and are a unique feature of this invention.
Effective functioning of a map is subjective; that is, the map is good if it transfers required information accurately and easily to the viewer. A line map gives no sense of altitude, unless it includes elevation contours, which require time for their interpretation. Visual image simulation gives an indication of elevation; but it requires somewhat complicated (and hence equipment-costly) computation and it conceals what lies beyond the next hill, which information may be the reason why a map is needed at all.